Ronaldo: United return isn't vacation, 'I am here to win again'
"I am not here for a vacation," the 36-year-old said in an interview on the club's website. "Before was good, winning important things and I wore the shirt before many years ago, but I am here to win again.
"I am capable, me and my teammates. I am ready to go, I am ready to go. It is a good chance for me, for the supporters, for the club, to get one step ahead.
"I am ready and I think I will be a huge thing in the next three or four years."
Ronaldo finalized his return to Old Trafford on Wednesday, putting pen to paper on a two-year contract.
The five-time Ballon d'Or winner scored 118 goals during his first stint with the Red Devils, which lasted six years before he departed for Real Madrid in 2009.
Ronaldo could potentially make his second debut for the club when Manchester United host Newcastle on Saturday.